Introduction to Raster Image Processing

Imposition is more intensive and generally applies to multi-page documents that require post bindery processing. For screen printers, imposition is more related to step-and-repeat work. It is very important for decal, tag, and label printers. Imposition can be very intensive and often is often supported through separate software that runs in conjunction with the RIP, although it may also be part of the RIP itself.

The next three image-related functions are color separation, trapping, and halftone screening. These functions are all specific to the RIP employed and are generally transparent to the user. What this means is that the user will define how they want the image separated, trapped, and screened, and the RIP makes all the decisions about how to achieve the desired characteristics.

User-defined parameters are stored as preferences, scripts, or routines in the RIP. When it comes time to send a job for output, the operator simply chooses the desired output device based on how the image will be used. The separation, trapping, and halftone screening are all done on the fly as the image is output.

The trend is clearly to incorporate this technology at the RIP level. In the past, these three functions were handled by dedicated applications that worked in conjunction with the RIP. As workflows become increasingly automated and technical labor becomes less available, however, the separation, trapping, and screening will almost surely become a standard component of the RIP.

Other RIP features are designed to allow for the smooth and efficient processing of large volumes of images. They provide accounting information and productivity information so that the maximum amount of work can be done on any given shift.

One of the big issues with digital files is the time it takes to process them. If ever there was a good example of the "time is money" principle, digital imaging is it.

Every operator who has ever output a large image is familiar with the job that takes hours to process before it crashes. In order to minimize the chances of this happening, it is necessary to preflight the images before sending them on for processing. Often this is done with standalone software, but there are an increasing number of preflight features being built into today's RIP software.

Besides finding missing and conflicting fonts and graphics, the preflight software looks for things like proper file format and image resolution based on how the file will be output. This is necessary to avoid over and underprocessing of data. With over processing, the images take too much time to process, data is discarded as redundant, and there is no visual advantage when the final print is delivered. With under-processed images, low resolution results in serious pixelization and artifacting (especially with JPEG images.)

In addition to the preflight functions, there are the time-reporting capabilities that log how long it took to RIP and image each job. This is especially useful for management in determining job estimates and if it will be necessary to charge additional fees for particularly difficult jobs. Long processing time is becoming an increasingly common problem with complex vector images that incorporate mesh gradients and transparent Postscript images. These two elements can bring almost any RIP to its knees.

The management productivity logs featured in most RIP software keep track of overall job performance and quantity over the day. They are used in production planning and job costing to help in profit analysis. They are useful in determining traffic trends and can be helpful in identifying processing patterns throughout the course of the day.

Conclusion

RIP functions will become more and more important to all of us as the use of in-house imaging increases. As the trend toward rapid job turnaround continues to pressure us, the efficient and integrated processing of digital images will be a key component of maintaining a profitable shop. A complete understanding of the capabilities of the RIP within this workflow is crucial for our success.